Method of molding coated articles of fibrous materials

ABSTRACT

A method of press-molding sheet-coated articles especially of a platelike shape from a mixture of comminuted fibrous materials and a thermosetting binder by impressing conical or similar recesses in the normally lower side of the material for increasing especially during the hot-molding operation the rate of compression of the material within the marginal areas and especially the corner areas of the fibrous body of the article so as to prevent any shrinkage of the material while it is setting and thereby to insure that the covering sheet material will be firmly bonded to the fibrous body especially within these areas. The projections on the molding die for impressing the recesses also act as gripping means to prevent the shrinking of the material.

United States Patent Munk Oct. 9, 1973 METHOD OF MOLDING COATED3,373,233 3/1968 Rondum 264/112 ARTICLES OF FIBROUS MATERIALS FOREIGNPATENTS OR APPLICATIONS [75] Inventor: Edmund E. Munk, Oberstenfeld,1,255,300 H967 Germany Germany [73] Assignee: Furnier-und SperrholzwerkJ. F. Primary R0bert F White Werz Jr. K.G. Assistant Examiner-J. R. HallWerzalit-Pressholzwerk Attorney-Michael S. Striker Oberstenfeld,Stuttgart, Germany Filed: May 3, 1971 [5 ABSTRACT Appl. No.: 139,535

Related U.S. Application Data [30] Foreign Application Priority Data May2, 1968 Germany P 17 03 323.1

[52] U.S. Cl. 264/112 [51] Int. Cl B29 5/04 [58] Field of Search264/112, 122

[56] References Cited UNITED STATES PATENTS 3,439,081 4/1969 Enderlein264/112 llIll/llI/II/IIIIII/II/I/I/IIII/fl/ A method of press-moldingsheet-coated articles especially of a platelike shape from a mixture ofcomminuted fibrous materials and a thermosetting binder by impressingconical or similar recesses in the normally lower side of the materialfor increasing especially during the hot-molding operation the rate ofcompression of the material within the marginal areas and especially thecomer areas of the fibrous body of the article so as to prevent anyshrinkage of the material while it is setting and thereby to insure thatthe covering sheet material will be firmly bonded to the fibrous bodyespecially within these areas. The projections on the molding die forimpressing the recesses also act as gripping means to prevent theshrinking of the material.

9 Claims, 5 Drawing Figures PATENTED 9|973' 3.784545 H6 20 & ib\\\\\\\\\\\\\ ATTORNE METHOD OF MOLDING COATED ARTICLES OF FIBROUSMATERIALS CROSS-REFERENCE TO RELATED APPLICATIONS The presentapplication is a continuation-in-part application of the copendingapplication Ser. No. 820,809, filed May 1, 1969 and now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to a method ofproducing molded articles which may have planar or uneven surfaces andangular, rounded or specially-shaped projecting edges and are made byapplication of heat and pressure to a mixture of comminuted organicfibrous materials, for example, wood chips, with a hot-setting binderand are coated with a thin decorative sheet material.

More particularly, the invention relates to improvements in the methodas disclosed by the present applicant in the patent granted in theFederal Republic of Germany, No. 1,255,300, and also in correspondingpatents granted in numerous other countries.

In this known method which is generally carried out in two steps, ablank of substantially the same shape as, but a slightly larger sizethan the finally molded article, is first produced by cold-molding, andin a subsequent hot-molding operation this blank is further compressedto its final shape and size, the coating material is molded thereon, andthe binder is set completely.

ln order to prevent the molded body as much as possible from shrinkingduring the setting of the molding mixture in the final hot-moldingoperation in which the thin sheet material is also bonded to the outersurfaces of the molded body, since such shrinkage would also cause thecovering sheet material to be unequally and insufficiently bondedtogether with the molded body, the known method as disclosed in thementioned German patent provides that the die for molding the normallylower side of the article is provided with projecting ridges forimpressing continuous or interrupted grooves into the molding materialwhich preferably extend parallel to and at a short distance from theedges of the molded body or from one or more projections on the otherside of the body. These grooves are usually impressed during thehot-molding operation, although they may also be partly premolded in thecold-molded blank. These projecting ridges on the die are designed sothat by molding the grooves they cause an additional compression of thematerial near the edges of the molded body and, if desired, also near aprojection on the normal plane of this body, and thereby prevent anysubstantial shrinkage of the molding material while it is setting,especially with respect to the covering-sheet material, by insuring thatthe back pressure'which has to be exerted upon the outer surface of thesheet material to bond the same to the molded body will be suffi-, cientat all points and especially near the edges and projections of the body.Aside from effecting such additional compression, the ridges on the diealso have the function of gripping the material while it is setting sothat also for this reason no substantial shrinking can occur.

la the mentioned patent it was already pointed out that the grooveswhich are to be molded into one side of the material should not exceed adepth of to 3.0 percent of the general thickness of the final article orof the part thereof on which a projection is formed because it was foundthat a deeper compression might result in a deformation of the coveringsheet material which would be noticeable on its outer side.

Although this method has proved to be of great advantage, it has beenfound that, especially near the corners of the molded body, the usualdepth of the grooves is often not sufficient in order to produce therequired back pressure which is necessary for securely bonding thecovering sheet material at all points to the molded body during thehot-molding operation. This, of course, applies especially if thesurface of the die is provided with at least a pair of projecting ridgeswhich extend, for example, at right angles to each other, but if forreasons of a more simple manufacture these ridges are not made of such alength that their adjacent ends join each other and form an apex so thatthe molded body would then be provided with a continuous rectangulargroove which extends parallel to two adjacent edges of the body and theapex of which is located adjacent to the rectangular corner betweenthese edges. Thus, since the two adjacent grooves are then separatedfrom each other within an area near the corner of the molded body, thiscorner area which, as has now been found, should actually be more highlycompressed than the other marginal areas will be devoid of anyadditional pressure and will thus be subject to shrinkage, and thecovering layer will therefore be bonded insufficiently to this cornerarea.

SUMMARY OF THE INVENTlON lt is an object of the present invention toovercome these disadvantages of the method as previously described andto insure that, by impressing recesses from the bottom face, andespecially at the corner areas of a molded article which is covered witha thin sheet material, the material within these areas will be so highlycompressed during the final hot-molding and bonding of the sheet to thecompressed material that a sufficient back pressure will also be exertedat these areas so that the sheet material will be securely bondedthereto. It is another object of the invention to impress recesses ofsuch a shape and in such a manner into the material of the molded bodythat, due to the shape of these recesses, they may be safely impressedto a considerably greater depth than the elongated groovelike recesseswhich were impressed by the knownmethod by projecting ridges on one ofthe dies. By impressing the recesses according to the invention not onlyin the corner areas from the bottom face of a molded article into thelatter, but also in other areas, for example, adjacent to the edges ofthe article or adjacent to projections on the other side of the article,all of these recesses may be impressed to a greater depth than that towhich the v groovelike recesses could be impressed by the known methodwithout danger that the covering sheet material might be deformed ormarked on its outer surface. A

For attaining these objects, the present invention provides especiallyeach corner area of the die with a conical or similar projection so asto impress a recess of a corresponding shape from the bottom face of themolded article into the latter at a point which is located 1 on thebisecting line of the angle which is formed by each of the angular orrounded corners of the article.

These conical corner recesses may be provided in combination withgroovelike recesses of the type, in accordance with the known method,which preferably extend parallel and adjacent to side faces of themolded body and may either terminate closely adjacent to the conicalcorner recess which is made of a greater depth than the groovelikerecesses or extend into the lower part of the conical corner recess.Since such a conical recess may be safely made of a considerably greaterdepth than the adjacent groovelike recesses, the comer area of themolded article will be more highly compressed in accordance with theinvention than the adjacent marginal parts so that the necessarypressure will also be produced within the angular or rounded corner areato secure the thin sheet material at all points firmly to the upper,lower and lateral faces of the corner area,

for example, ofa plate-shaped element. By making at least each of thesecorner projections on the die and the corresponding recesses in themolded article of a conical or similar tapering shape, the pressurecomponents will be distributed within the article in such a manner thatthe covering layer will not be deformed or marked on its outer side eventhough the depth of the recess from its free outer end to its point-likeinner end is made much larger than the depth of one of the groovelikerecesses.

The angle of the taper of each conical projection on the die, andespecially of each corner projection, is made of such a size that thebase diameter of this projection which corresponds to and produces themaximum diameter of the conical recess at the free end thereof isconsiderably larger than the width of the base of one of the ridgelikeprojections for molding one of the groovelike recesses. This is trueespecially when a conical corner recess is employed in combination withtwo adjacent groovelike recesses which extend parallel to the adjacentedges of the molded article, and it is also true regardless of whetherthe ends of these groovelike recesses are spaced at short distances fromthe free outer end of the conical corner recess or whether theyterminate in the free outer end of the corner recess.

It-is another feature of the invention to provide the molded articlewith a row of conical recesses in place of a longer continuousgroovelike recess or in place of several shorter groovelike recesseswhich are separated by ungrooved portions. This has the advantage thatdue to their shape the conical recesses forming such a row may also bemade of a considerably greater depth and a greater width at their outerends than the groovelike recesses. Such rows of conical recesses may beemployed in combination with conical corner recesses by extendingsubstantially parallel to the adjacent edges of the molded article, inwhich event, however, the conical corner recesses should preferably bemade of a greater depth and a greater maximum diameter than those of theadjacent rows. Such a row of rows of recesses may, however, also beimpressed into one side of the article to compress the same more highlyatanother area or other areas which are provided with a projection orprojections on the opposite side of the article. The adjacent conicalrecesses of such a row may also merge into each other at their largerouter ends, and if employed in combination with larger conical cornerrecesses, the smaller conical recesses next to such a corner recess mayalso merge partly into the free end of the larger corner recess.

Although previously and hereafter the recesses according to theinvention as well as the die projections for producing these recessesare described as being of a conical shape tapering to a point, they mayalso be of another tapering shape, for example, of the shape of apyramid with three or more sides. It is also not absolutely necessarythat they taper to a point, but they may also terminate in a smallrounded inner end or in a small flat surface.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 shows a bottom view of a cornerpart of a plate which is produced in accordance with the invention;

FIG. 2 shows a cross section which is taken along line II-II of FIG. 1,and in which, for better illustration, the covering layer is shown of athickness considerably greater than its actual thickness;

FIG. 2a shows a partial cross sectional view of a die for forming theplate partially shown in FIGS. 1 and 2;

FIG. 3 shows a bottom view ofa corner part of a plate according to amodification of the invention; while FIG. 4 shows a bottom view of acorner part of a plate according to a further modification of theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 and 2 of the drawingsillustrate one corner part of a plate 3 which is produced in accordancewith the present invention. Plate 3 is provided with groovelike recesses6 which are impressed into the lower side of the plate and each of whichextends substantially parallel to and at a certain distance from theadjacent outer edge up to a point near each corner of the plate. Each ofthese corner parts of plate 3 is provided with a conical recess 7 whichis separate from the adjacent grooves 6 and has at its outer end amaximum diameter dwhich is larger than the maximum width b of the outerside of the grooves 6. The body of plate 3, which is molded from amixture of comminuted fibrous materials, for example, wood chips, and athermosetting binder in the form of a natural or synthetic resin, iscovered on all sides,,with the exception of the deeper inner surfaces ofthe conical recess 7, and possibly also of the bottom of grooves 6, witha continuous layer 4 and 5 of a suitable sheet material which is bondedtogether with the body of plate 3 by the hot-molding operation. By thedifferent density of the lines indicating the fibrous mixture of thebody of plate 3, FIG. 2 illustrates the higher rate of compression Vwhich is attained within the corner area of plate 3 by impressing theconical recess 7 into its lower side to a depth T which is considerablydeeper than the depth 1 of the adjacent grooves 6.

The plate 3 described above and illustrated in part in FIGS. 1 and 2, inpress-molded in a two-part mold or die D and D; as illustrated in FIG.2a which, when closed, as shown in FIG. 2a, defines a mold cavity C. Thelower-mold part D is provided with ridges 6' projecting upwardly fromthe upper surface of the lowermold part, and are inwardly spaced fromand substantially parallel to the side faces thereof which define themold cavity C. These ridges 6 end short of the corner portions of thecavity, and a substantially conical projection 7 is provided in theregion of each corner portion of the cavity and likewise projectsupwardly from the upper surface of the mold part D A preformed blank ofa mixture of comminuted fibrous material and a thermosetting binder,covered on all sides except for the abovenoted exceptions with acontinuous layer of a suitable sheet material, is placed between the twoparts of the mold and the latter is then closed under application ofheat and pressure thereto to harden the thermosetting binder and at thesame time to bond the sheet material together with the body of the plate3. During closing of the mold, the ridges 6 and the conical projections7 will penetrate into the bottom face of the blank to provide the latterwith groovelike recesses 6 and conical recesses 7 as described above.Thereby, the comminuted fibrous material is more highly compressed inthe region of the ridges 6, and especially in the region of the conicalprojections 7', which have, as shown in FIG. 2a, a height greater thanthat of the ridges. This greater compression of the blank in the regionof the ridges and the conical projections will prevent shrinking of theplate during setting of the molding mixture in the final hot moldingoperation, especially since the aforementioned ridges and projectionswill penetrate during such molding operation into the recesses formedthereby. This in turn, will assure proper bonding of the outer sheet tothe body of the plate 3 during the hot molding operation since anyrelative shifting of the adjacent surfaces of the outer sheet and thebody of the plate during the final hot molding operation is thusprevented.

FIG. 3 shows a bottom view of a corner part ofa plate 3 which isprovided with groovelike recesses 6 and deeper conical corner recesses 7according to a modification of the invention. The ends of grooves 6,which again extend substantially parallel to the outer edges of plate 3,merge into the wider lower parts of the corner recesses 7. Or course, itis also possible to extend only one of the grooves 6 into the lower partof the conical corner recesses 7, while the other groove 6 terminates ata short distance from this corner recess 7.

The mold for producing the plate shown in part in FIG. 3 is similar tothe mold described above in connection with FIG. 20, but differstherefrom in that, in this case, the ridges in the bottom part of thetwo-part mold extend up to and are joined to the conical projectionprovided at each comer.

FIG. 4 shows a bottom view of a corner part of another plate 3 into thelower side of which two rows of conical recesses 8, which extendsubstantially parallel to the adjacent edges of plate 3, are impressedin place of the grooves 6 as shown in FIGS. 1 and 2. Since, according tothe invention and for the reasons as previously stated, the conicalcorner recesses 7 are preferably made deeper than the recesses 8adjacent to the lateral edges of plate 3, the diameters of the outerends of the corner recesses 7 are preferably also made larger than thoseof the recesses 8 of the lateral rows. However, if desired, thediameters of the outer ends and/or the depths of all of the conicalrecesses 7 and 8 may also be made of the same size or sizes.

The mold for producing the plate partly shown in FIG. 4 is similar tothe mold described above in connection with FIG. 2a but, instead oflongitudinal ridges 6, there are provided rows of substantially conicalprojections for forming the recesses 8 which have, however, a smallermaximum diameter and a shorter height than the corner projections forforming the recesses 7 at each comer of the plate.

As has also been previously mentioned, the recesses 7 or 8 may also bemade of a tapering shape other than conical, for example, of a pyramidalshape with three or more sides. In such an event, it may be of advantageto make the different sides of each pyramid of different inclinationsrelative to the plane surfaces of the upper and lower sides of plate 3,for example, by making the sides of the pyramids facing the outer edgesand corners of the plate of a steeper inclination than the inwardlyfacing sides. Of course, if the recesses 7 or 8 are made of a conicalshape, their axes may be similarly inclined toward the corners or towardthe lateral edges of plate 3.

Although my invention has been illustrated and described with referenceto the preferred embodiments thereof, I wish to have it understood thatit is in no way limited to the details of such embodiments but iscapable of numerous modifications within the scope of the appendedclaims.

Having thus fully disclosed my invention, what I claim is:

l. A method of making from a mixture of comminuted fibrous material anda thermosetting binder a substantially plate-like polygonal elementhaving a top face, a bottom face and a plurality of side faces extendingat angles relative to each other and defining a plurality of edges andcorners of said element, comprising:

a. press-molding from said mixture said element under application ofheat and pressure thereto with a thin cover sheet applied to respectivefaces thereof;

b. compressing said element while activating said thermosetting binderand simultaneously impressing into said element along edges of saidbottom face thereof recess means having a predetermined depth andextending parallel to the respective edges, and in the region of eachcorner thereof a corner recess opening in said bottom face and taper-ingin direction towards said top face substantially to a point and having adepth greater than said predetermined depths of said recess means; and

C. maintaining the thus compressed and impressed element in compressedcondition at least until said activated thermosetting binder has set soas to bond said fibrous material and said cover sheet thereto and toprevent shrinkage of said element in said corner regions thereof duringsaid setting of said thermosetting binder.

.2. A method as defined in claim 1 wherein each of said corner recesseshas a conical shape.

3. A method as defined in claim 1 wherein each of said corner recesseshas a pyramidal shape having at least three sides.

4. A method as defined in claim 1 wherein each of said corner recessesis impressed into said element so as to have at said bottom faceadimension'greater than the width of said recess means at said bottomface.

5. A method as defined in claim 1 wherein said recess means areimpressed in the form of elongated grooves.

6. A method as defined in claim wherein said grooves are impressed insuch a manner that they end short of said corner recesses 7. A method asdefined in claim 5 wherein said 8. A method as defined in claim 1wherein said recess means are in the form of a row of consecutiverecesses.

9. A method as defined in claim 8 wherein each of grooves are impressedin such a manner that they inter- 5 sad conseiutwe recesses has aconical p sect said corner recesses.

1. A method of making from a mixture of comminuted fibrous material anda thermosetting binder a substantially plate-like polygonal elementhaving a top face, a bottom face and a plurality of side faces extendingat angles relative to each other and defining a plurality of edges andcorners of said element, comprising: a. press-molding from said mixturesaid element under application of heat and pressure thereto with a thincover sheet applied to respective faces thereof; b. compressing saidelement while activating said thermosetting binder and simultaneouslyimpressing into said element along edges of said bottom face thereofrecess means having a predetermined depth and extending parallel to therespective edges, and in the region of each corner thereof a cornerrecess opening in said bottom face and tapering in direction towardssaid top face substantially to a point and having a depth greater thansaid predetermined depths of said recess means; and c. maintaining thethus compressed and impressed element in compressed condition at leastuntil said activated thermosetting binder has set so as to bond saidfibrous material and said cover sheet thereto and to prevent shrinkageof said element in said corner regions thereof during said setting ofsaid thermosetting binder.
 2. A method as defined in claim 1 whereineach of said corner recesses has a conical shape.
 3. A method as definedin claim 1 wherein each of said corner recesses has a pyramidal shapehaving at least three sides.
 4. A method as defined in claim 1 whereineach of said corner recesses is impressed into said element so as tohave at said bottom face a dimension greater than the width of saidrecess means at said bottom face.
 5. A method as defined in claim 1wherein said recess means are impressed in the form of elongatedgrooves.
 6. A method as defined in claim 5 wherein said grooves areimpressed in such a manner that they end short of said corner recesses.7. A method as defined in claim 5 wherein said grooves are impressed insuch a manner that they intersect said corner recesses.
 8. A method asdefined in claim 1 wherein said recess means are in the form of a row ofconsecutive recesses.
 9. A method as defined in claim 8 wherein each ofsaid consecutive recesses has a conical shape.